Results not clear cut in Southern Ocean experiment

An experiment off the coast of Antarctica has lent support to the notion that scientists could stimulate algae to act like a giant sponge and sop up greenhouse gases in the atmosphere.

In the study, reported in Thursday's issue of the journal Nature, a relatively small amount of iron was pumped into the ocean as fertilizer, sparking algae growth in an otherwise lifeless area.

The algae in turn consumed hundreds of tons of carbon dioxide from the ocean's surface waters. Then, in theory at least, the ocean would draw in atmospheric gases to replenish the carbon dioxide.

The idea is that algae could someday be used to absorb emissions belched from factories, cars and other fossil fuel burners believed responsible for global warming. When the organisms died, the carbon they contained would fall to the bottom of the sea.

Though the latest studies support parts of the theory, researchers could not determine whether the carbon sinks or returns to the atmosphere. And some fear that manipulating nutrients in the sea could cause greater damage.

''I don't think it's a feasible solution to global warming,'' said Edward Abraham, a study author and oceanographer at New Zealand's National Institute for Water and Atmospheric Research.

''Even if you could fertilize the entire Southern Ocean and even if all that carbon sank out of the system, it would only use a small fraction of the carbon dioxide that people will pump into the atmosphere over the next 50 years.''

Researchers are exploring ways to trap at least some of the 7 billion tons of carbon dioxide and other greenhouse gases spewed into the atmosphere each year. Some ideas include pumping it underground or piping it to the deep ocean.

At least three patents have been issued related to ocean fertilization. Researchers have focused on ocean plant life because half of all carbon dioxide-consuming photosynthesis on Earth takes place at sea.

In 1990, oceanographer John Martin suggested a lack of iron limited the growth of phytoplankton in the equatorial Pacific and Southern Ocean. If more iron were added, the populations might explode and ease global warming.

In the latest research, eight tons of an iron slurry were distributed across a five-mile-wide patch of the Southern Ocean about 1,200 miles southwest of Hobart, Tasmania.

As in previous tests in the equatorial Pacific, phytoplankton and carbon levels increased steadily in the waters over the 13 days of monitoring in 1999. Satellite data showed the bloom grew to more than 93 miles long after six weeks, accumulating anywhere from 660 to 3,300 tons of algal carbon.

But because of the experiment's tight schedule, nobody could monitor the algae when it eventually died. It was not clear whether carbon leaked back into the atmosphere or was drawn to the ocean depths.

Also, there is fear the spurt of growth in the fertilized area might affect the waters outside the patch. Other nutrients such as nitrogen and phosphates might be sucked in, canceling any growth that would have occurred outside. Or iron-enriched plankton might poison other life.

''My big concern is that the uncertainties are just incredibly large,'' said Sallie Chisholm, a researcher at the Massachusetts Institute of Technology.